The invention relates to a magnetic coupling, in particular a magnetic coupling pump comprising an inner rotor and an outer rotor, which each carry magnets between which a split case is disposed, which has a flange, which flange can preferably be fixed with a counter-flange on a coupling component, preferably on a casing cover.
Magnetic coupling pumps are generally known and described, for example, in DE 10 2009 022 916 A1. In this case, the pump power is transmitted from a drive shaft via a magnet-carrying rotor (outer rotor) in a contact-free manner and substantially free from slippage onto the pump-side magnet carrier (inner rotor). The inner rotor drives the pump shaft which is mounted in a sliding bearing lubricated by the conveying medium, i.e. in a hydrodynamic sliding bearing. Located between the outer rotor and the inner rotor, i.e. between the outer and the inner magnets is the split case with its cylindrical wall. The split case is connected with its flange to a pump component, for example, a casing cover and has a closed base opposite thereto. The split case, i.e. the magnetic coupling pump reliably separates the product case from the environment so that the risk of an escape of product with all the associated negative consequences can be eliminated. A magnetic coupling pump is accordingly the combination of a conventional pump hydraulics with a magnetic drive system. This system uses the attraction and repulsion forces between magnets in both coupling halves for the contact-free and slippage-free transmission of torque. The magnetic coupling pump accordingly has major advantages particularly when handling very valuable or very hazardous substances.
Split cases can consist of different materials such as, for example, of metals having most diverse alloy compositions. Split cases made of metal disadvantageously cause eddy current losses, whereas plastic split cases have only limited temperature and/or pressure resistance, which is particularly disadvantageous at high medium temperatures and/or high pump pressures. In this respect, ceramic split cases have proved successful in practice, with split cases made of glass also becoming known recently (DE 10 2009 022 916 A1).
The split case is connected via its flange to the pump component or to the coupling component, for example, screwed and thus forms a sealed connection, possibly with a seal (O-ring) interposed. The pump component and also the counter-flange consist of a metal material which each have different material properties to the ceramic of the split case, where for example mention should be made of different (thermal) expansion coefficients. In this respect, tensions can occur under thermal stressing of the metal-ceramic connection, where the metal connection partners expand more than the ceramic connection partners. These expansions are passed into the originally tight contact surface between the flange and the pump component so that the originally sealed connection can have leaks since the seal provided (O ring) is as it were relaxed. For example, an edge loading can occur where the metal component presses into the ceramic flange and can thus destroy this (incipient cracking). However extreme caution is also required during assembly, i.e. when screwing the split case onto the pump component since the ceramic of the split case reacts very sensitively to unfavourable stress transitions or stress peaks, i.e. to nonuniform tightening of the screws and can also be destroyed.